Vitamin A deficiency is the leading cause of childhood blindness worldwide. With increasing deficiency the cornea becomes keratinized and is susceptible to corneal ulceration (keratomalacia). Vitamin A deficient children, because of an increased susceptibility to infections, have higher morbidity and mortality rates than their normal peers from the same geographical area. Understanding why the inflammatory process is abnormal is important in the treatment of a vitamin A deficient child. The long term goal of this project is to elucidate the effects of vitamin A deficiency on the inflammatory process in the cornea. This grant is directed towards the polymorphonuclear leukocyte, a major mediator of corneal inflammation. The specific aims are the following: 1) To determine the time course of the effects of vitamin A deficiency on corneal and in vitro tested polymorphonuclear leukocyte functions. 2) To determine the ability of in vitro added retinol, retinoic acid and retinal to restore in vitro tested polymorphonuclear leukocyte function. 3) To determine the effect of in vivo administered therapeutic doses of vitamin A on corneal and in vitro tested polymorphonuclear leukocyte function 1, 2, 8 and 16 days after administration. 4) To determine which reactions involved in polymorphonuclear leukocyte function are altered. The rat model of vitamin A deficiency will be used at early, mid and late deficiency. In vivo function will be tested using the corneal model of Pseudomonas keratitis with a strain of Pseudomonas aeruginosa chosen for its ability to induce a controlled polymorphonuclear leukocyte response. Peripheral PMNs will be characterized in vitro as to their number and maturity, stability in the resting and active states, ability to chemotax towards a stimulus, phagocytose, kill and digest bacteria under stimulated and non-stimulated conditions. Reactions and/or mechanism involved in PMN activation, killing, digestion and self-protection will be addressed. Light and electron microscopy, fluorescence cytoflow, enzymatic and cell biology techniques will be used.